In the context of immune response, what is the role of helper T cells?

A. It helps in the transportation of oxygen across the alveolar membrane: Oxygen transport across the alveolar membrane depends on diffusion driven by concentration gradients, not directly on surfactant.

B. It increases the rate of oxygen absorption in the lungs: Surfactant does not directly increase oxygen absorption; it facilitates gas exchange indirectly by maintaining alveolar stability.

C. It reduces surface tension to prevent alveolar collapse: Surfactant is a lipid-protein substance that lines alveoli, lowering surface tension. This prevents alveolar collapse during exhalation and allows easier expansion during inhalation, improving overall lung function.

D. It supports the structural integrity of the bronchial walls: Bronchial walls are supported by cartilage and smooth muscle, not surfactant, which primarily functions within the alveoli.

A. Ball and socket joints: Ball and socket joints, such as the shoulder and hip, allow for a wide range of movement in multiple directions. They are synovial joints with a fluid-filled cavity, not primarily connected by cartilage for limited motion.

B. Synovial joints: Synovial joints have a joint cavity filled with synovial fluid and permit free movement. They include hinge, pivot, and ball-and-socket joints, providing more mobility than partial-movement joints.

C. Cartilaginous joints: Cartilaginous joints are connected by cartilage, allowing limited or partial movement. Examples include intervertebral discs and the pubic symphysis, providing stability while permitting slight flexibility.

D. Fibrous joints: Fibrous joints are connected by dense connective tissue and allow little to no movement. Examples include sutures in the skull, which provide strength and protection rather than flexibility.